Suppose f is a coordinate function for l=(line) AB such that f(A)=0 and f(B)>0. Prove that (ray) AB={P (is an element of) l such that f(P) >=0}

Hint: the definition of ray: the ray AB is the set of points = Segment AB union {P: A*B*P}

HELP PLEASE. This all has to do with Neutral Geometry if that helps any.